The present invention relates to a device for applying an adhesive to the spine region of an inner book that projects from a clamp or the like as the book is conveyed in a transport system.
Devices of this type include at least one rotating application roller or application disc which picks up adhesive from a reservoir and transfers the adhesive to the inner book by rolling-off, a doctor blade adjustable relative to the application roller for regulating the application thickness of the adhesive, and an actuating device for the controlled movement of the doctor blade between an application position and a zero-application position.
Various application systems in adhesive binding machines are available for mechanically applying an adhesive to the spine and adjacent areas of the side faces of inner books together or in the alternate also referred to herein as the “spine region”. Wheel glue application mechanisms are very often used, wherein the embodiments for spine gluing are referred to as (cylindrical) roller mechanisms, while the embodiments for applying glue to the sides are referred to as discs. Roller gluing mechanisms consist predominantly of a first roller for applying a thin layer of adhesive and a second roller for applying a thick layer of adhesive. For leveling and removing surplus adhesive from the spine of the inner book a spinner roller which rotates in the opposite direction to the transport direction of the inner books is arranged downstream of both the above-mentioned rollers. Doctor blades adjustable with respect to the roller surface are provided for metering the thickness of the adhesive applied to the rollers. A roller gluing mechanism of this kind for spine gluing is schematically represented, for example, in Liebau, Heinze: Industrielle Buchbinderei, Verlag Beruf+Schule, Itzehoe 2001, Ch. 4.2.3.3.6, pp. 284 ff.
A side-gluing mechanism with application discs is described, for example, in DE 200 08 757 U1. The adhesive is located in a reservoir below the transport plane of the inner book and is conveyed upwardly into the gluing area by means of a helical adhesive scraper surrounding the application discs. Here the application thickness of the adhesive is regulated by doctor blades.
The doctor blades are switched or controlled back and forth between an application and a zero-application position synchronously with the inner book conveyance. Application of the adhesive begins when the inner book passes over the rollers or discs and ends before the end of the inner book leaves the approach area of the rollers. This avoids adhesive banked up at the start from depositing on the front face of the inner book and adhesive projecting from the inner book through thread formation at the end. In addition, the adhesive must be applied offset from the beginning and end of the inner book, so that adhesive is not squeezed out when the cover is pressed on. The offset adhesive application also minimises contamination of the trimmed waste with adhesive. For high-quality adhesive binding start and finish points of the glue application positioned precisely at the beginning and end of the inner book are required. The flank at the start and finish of the adhesive layer must be as steep as possible. Especially in the case of adhesive binders with high transit velocities, this necessitates a very fast (dynamic) movement of the doctor blade between the application and zero-application positions.
In the case of known wheel gluing mechanisms the doctor blades are controlled by cams. The start and finish positions for the adhesive layer are embodied in a fixed manner in the cams. To adjust the length and position of the adhesive layer complex designs with variable transmissions are required, or the adjustments can only be carried out with the adhesive binder at a standstill. Layer patterns or the omission of the adhesive layer at the separation point of an inner book manufactured two copies are possible only by replacing the cams by cams specially in configured for this purpose. With pneumatic actuation of the doctor blades the adjustment can be effected electrically and special layer patterns are possible with suitably constructed control devices. For example, a wheel gluing mechanism for side-gluing with pneumatically actuated doctor blades is illustrated in JP 09-086070. However, ordinary pneumatic cylinders have imprecise switching times, making it impossible to apply adhesive precisely, especially at high transit velocities of the inner book. Because of the poor dynamic behaviour of the pneumatic cylinders the start and finish points are not sharply defined.